1. Field of the Invention
The invention relates to surgical devices and in particular to instruments used in the arthroscopic repair of ligaments such as anterior cruciate ligaments. More particularly, the invention relates to instruments for securing grafts such as artificial natural or prosthetic ligaments in bone tunnels while protecting the ligament from damaging by the securing device.
2. Description of the Prior Art
As new procedures and instruments continue to be developed for arthroscopically repairing knee ligaments such as anterior cruciate ligaments (ACLs) and posterior cruciate ligaments (PCLs) and as surgeons become familiar with these existing procedures, the need for other new devices becomes apparent.
For example, it is becoming fairly common to repair an ACL with an autograft ligament formed of bone-tendon-bone harvested from the patient's patellar bone, patellar tendon and bone from the tibial tuberosity. Such a graft ligament (which may be an allograft) takes the form of an elongated, natural ligament which has generally rectangularly shaped natural bone blocks at each end. One procedure for accomplishing an arthroscopic ACL repair with such a graft ligament is disclosed in U.S. Pat. Reissue No. 34,293 (Goble et al.), incorporated by reference herein, which describes a surgical method comprising the steps of securing a natural or prosthetic ligament endosteally within a "blind" tunnel segment formed in the femur and an aligned tunnel segment formed in the tibia, both tunnel segments formed through a single incision. In addition to the various ligament fixation devices disclosed in the aforementioned patent, many ACL repair procedures utilize bone-tendon-bone grafts secured by cannulated interference screws guided along elongated guide pins or guide wires into the space between the tunnel wall and the adjacent bone block in order to create an interference fit to retain the bone block within the tunnel. Such a procedure is described in U.S. Pat. No. 4,927,421 (Goble et al.), also incorporated by reference herein.
As surgeons have become adept at performing the aforementioned procedures, a need has become apparent for an improvement by providing a means to protect the graft or artificial ligament as it is being secured within the bone tunnel. Utilizing prior art devices it has been found that the ligament portion of the graft may occasionally be inadvertently cut or nicked by the interference screw threads, thus weakening the attachment of the artificial ligament within the bone. One type of graft protection device has been disclosed in U.S. Pat. No. 5,211,647 (Schmieding) which discloses an elongated, cylindrical cannulated sheath for retaining an interference screw within its distal end. The sheath is formed from plastic and has a portion of its distal tip removed in order to form a cutout through which the threads of the interference screw are exposed in order to enable them to grab the bone as the screw is turned relative to the sheath. The non-cutout portion of the sheath tip lies between the screw and the graft in order to keep the screw from damaging the graft. A screw driver is inserted axially through the sheath and into a drive recess within the interference screw in order to enable the screw to be advanced from the sheath. This device has proven to have too large a diameter for many applications, thereby making it difficult to insert the sheath tip through an opening in the skin and into the joint. This may result in the screw being prematurely pushed out of the sheath by the driver. The small cutout size makes it difficult to reassemble the sheath and screw, especially within the joint. The large size of the device also interferes with the surgeon's visualization of the work site.
Accordingly, it is an object of this invention to produce a graft protection device which overcomes the disadvantages of prior art devices.
It is another object of this invention to produce a graft protection device which provides adequate graft protection while minimizing the size of the device which may lie adjacent an opening in the skin through which the device must extend into a joint.
It is another object of this invention to provide a graft protection device for arthroscopic use with an interference screw wherein the device minimizes the arcuate coverage of the screw while still providing adequate graft protection and adequate retention of the screw on a driving device.
It is also an object of this invention to provide a graft protection device provided with a means by which the interference screw may be retained on the screw driver.
It is also an object of this invention to provide a graft protection device which may be easily moved by a user in order to adjust the longitudinal and rotational position of the device along the shaft of a screw driver.
It is another object of this invention to provide a graft protection device which may perform its intended function while optimizing the surgeon's ability to visualize the work site.